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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

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302                        FUELS  (GENERAL METHODS)

a mark at two litres, and a brass foot fitted with a small cylindrical copper
capsule or furnace in which the combustion occurs. The capsule is covered
with a copper cylinder with a row of holes round the bottom and a tube
with a tap at the top ; this cylinder is held in place by four springs on the
brass foot. A thermometer reading to 0-1, and protected by a metal guard,

is also required.

2 grams of the fuel, ground in an iron mortar to pass through a No. 6
sieve (650 meshes per sq. cm.), are thoroughly mixed on a piece of shining
paper by means of a flexible steel spatula with the oxidising mixture (3
parts of powdered, dry potassium chlorate and i part of potassium nitrate,
carefully mixed without using the iron mortar and passed through a No. 6
sieve), sufficient of the latter being used to give a homogeneous, lead-grey
mixture, which should burn completely, regularly and moderately rapidly.
The amount of oxidising mixture necessary is usually 20-30 grams per 2
grams of fuel, but it varies with the character of the fuel and should be

determined by preliminary trial.

By means of the spatula used before, the
mixture is placed in the coppei capsule in
such a way as to compress it uniformly and
as little as possible ; if the quantity of the
mixture is too great to be held by the capsule
without compression, it is advisable to use
only I gram of the fuel and the corresponding
amount of the oxidising mixture. On the
top of the mixture is placed a piece of slow
match,1 which should protrude about a
centimetre, the copper cylinder fitted, the
tap closed and the whole immersed in the
water in the glass cylinder; the water
should be, according to circumstances, be-
tween 2 and 7 lower than the temperature
of the air.2 The water is mixed by means of the apparatus itself and the tem-
perature shown on the thermometer noted; the apparatus is then with-
drawn, the match lighted, the cover rapidly replaced and the whole at
once placed in the water before the mixture ignites. After a few seconds,
when ignition occurs, the gaseous products issue turbulently from the holes
in the cover and escape upward through the water.

At the end of the combustion, which, if regular, requires one or two
minutes, the tap is opened, the tube unstopped by means of an iron wire
and the water stirred with the apparatus, the highest temperature reached
being observed. The rise of temperature, increased by one-tenth to correct
approximately for the losses and for the heat absorbed by the apparatus,
is multiplied by the weight of water in the glass cylinder. The product

1  Made from cotton lighting wick (or better of de-fatted jute) immersed in con-
centrated potassium nitrate solution and dried in an oven.

2  For ordinary air temperatures, the temperature of the water should be as follows :

Air temperature          .        .    10         15          20          25          30

Water temperature     .        ..    7-9        11-9        *5'90        197        23'2

FIG. 34ric acid and precipitated